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On the origin of 24-norcholestanes and their use as age-diagnostic biomarkers

Sebastiaan W. Rampen^*,1, Stefan Schouten¹, Ben Abbas¹, F. Elda Panoto¹, Gerard Muyzer^,1, Christine N. Campbell², Johanna Fehling^,2 and Jaap S. Sinninghe Damsté³

¹ Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands
² Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Dunbeg, OBAN, Argyll PA37, Scotland
³ Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands

24-norcholestanes have been shown to be useful biomarkers to assess the age of sediments and petroleum, but until now, the biological sources of their precursors, i.e., 24-norsterols, were unclear. We have unambiguously identified relatively high concentrations of 24- norcholesta-5,22-dien-3ß-ol in the diatom Thalassiosira aff. antarctica (6%–10% of total sterols) and, in much lower concentrations, in the dinoflagellate Gymnodinium simplex (0.2% of total sterols). These identifications and other reports of 24-norsterols in dinoflagellates suggest that both diatom and dinoflagellate species are major sources for 24-norcholestanes in sediments and petroleum. The evolutionary history of these organisms suggests that observed increases of 24-norcholestane concentration in the Jurassic and the Cretaceous are related to dinoflagellate expansion, whereas an increase in the Oligocene-Miocene is likely caused by diatom expansion. Our results also explain the biogeographical distribution of 24-norcholestanes, i.e., high concentrations at high (paleo)latitudes are likely caused by diatoms, while low concentrations at lower (paleo)latitudes are likely caused by dinoflagellates.

Key Words: age-diagnostic biomarkers • sterols • marine • diatoms • dinoflagellates